1. Field of the Invention
The present invention relates to methods for manufacturing a shoe for a refrigerant compressor. More particularly, it relates to methods for manufacturing a shoe for a swash plate-type compressor of a vehicle.
2. Description of the Related Art
In FIG. 1, a swash plate-type compressor 1 having shoes 151 is depicted. An outer shell of compressor 1 comprises front cylinder head 121, front valve plate 141, front cylinder block 99, rear cylinder block 100, rear valve plate 131, and rear cylinder head 142. A drive shaft 112 extends along the main axis of compressor 1. One portion of drive shaft 112 is rotatably supported by first boss 99b of front cylinder block 99 by needle bearing 113. Another portion of drive shaft 112 is rotatably supported by second boss 100b of rear cylinder block 100 by needle bearing 114. Swash plate 115 is fixed to drive shaft 112 by a screw 116 on boss 115b of swash plate 115. In order to prevent axial movement of drive shaft 112, a thrust bearing 117 is provided between first boss 99b of front cylinder block 99 and third boss 115b of swash plate 115. Further, a thrust bearing 118 is provided between second boss 100b of rear cylinder block 100 and third boss 115b of swash plate 115 to prevent axial movement of drive shaft 112.
Front cylinder block 99 and rear cylinder block 100 have a plurality of peripherally located cylinder chambers 119, within which pistons 101 reciprocate. Pistons 101 are connected to swash plate 115 through shoes 151 that are in contact with surfaces 115a of swash plate 115.
The centers of pistons 101 are formed to include a recessed portion 110a, to which axial end spherical sockets 110b are bored. Shoes 151 have hemispherical shapes. The bottom plane surfaces of shoes 151 contact surface 115a of swash plate 115. The spherical surfaces of shoes 151 engage the surface of spherical sockets 110b of pistons 101.
Swash plate 115 rotates with the rotation of drive shaft 112. When swash plate 115 rotates, shoes 151 slide on surface 115a of swash plate 115 and performs a precision movement within spherical socket 110b. Thus, shoes 151 transfer an axial component of the movement of swash plate 115 to pistons 101, and, concurrently, prevent the transfer of the rotational component of the movement of swash plate 115 to pistons 101.
Three methods for manufacturing shoes are described in Japanese patent publications S56-136249, S56-139248, and H1-162534.
In FIGS. 2a-d, a first method for manufacturing a shoe 151 is depicted. With reference to FIG. 2a, a cylindrical shaped material 119 is punched from a plate material (not shown.) According to this method, short cylindrical material 119 may be made of single material. Main portion 119a of cylindrical material 119 may be iron and base plate portion 119b may be copper. With reference to FIG. 2b, the upper edge of material 119 is circumferentially beveled to form conical surface 119c. With reference to FIG. 2c, material 119 has a beveled upper circumferential edge and is forged within upper forging die 123 and lower forging die 121. In the lower surface of upper forging die 123 is a spherical recess 124, and in the upper surface of lower forging die 121 is a shallow cylindrical recess 122, receiving the lower portion of material 119 and having substantially the same diameter of the lower pan of the material 119. This step forms a final shape of shoe 151. FIG. 2d depicts the completed forging process.
In the forging process, a phenomenon known as spring back may occur. By removing the forging force after the forging process, an amount of deformation is relieved, so that the intended dimension is not achieved. In order to suppress the spring back phenomenon, techniques to decrease the amount to be deformed may be performed. Beveling to form a conical surface, as indicated in FIG. 2b, is one such techniques. However, this beveling process consumes manufacturing time and increases costs of manufacturing shoes.
In FIGS. 3a-d, a second method for manufacturing shoe 151 is depicted. With reference to FIG. 3a, a cylindrical shaped material 119 is punched from a plate material (not shown.) With reference to FIG. 3b, the upper surface of main portion 119a of cylindrical material 119 is drilled to an intermediate point. The drilling process forms hole 120. With reference to FIG. 3c, material 119, is formed by upper forging die 123 and lower forging die 121. In the lower surface of upper forging die 123 is a spherical recess 124, and in the upper surface of lower forging die 121 is cylindrical recess 122. Cylindrical recess 122 receives the lower portion of material 119, and has substantially the same diameter as the lower portion of material 119. This step forms the final shape of shoe 151. FIG. 3d depicts the completed forging process. To suppress spring back phenomenon after the forging process, the drilling process depicted in FIG. 3b is performed. The drilling process, however, consumes manufacturing time and increases costs for manufacturing shoes.
In FIGS. 4a and 4b, a third method for manufacturing shoe 230 is depicted. With reference to FIG. 4a, a spherical material 223 is depicted. Upper hemisphere 223U of spherical material 223 faces cylindrical recess 220U. Cylindrical recess 220U is on the lower surface of upper forging die 220. Lower hemisphere 223L of spherical material 223 faces spherical recess 213L. Spherical recess 213L is on the upper surface of lower forging die 213. A rod 216 is used to push shoe 230 from spherical recess 213L of lower forging die 213 after the forging process has completed. FIG. 4b depicts the completion of the forging process. Referring to FIGS. 4a and 4b, upper hemisphere 223U is shaped to form a bottom plane surface 230P of shoe 230 by the forging process. Lower hemisphere 223L is shaped to form spherical surface 230S. The difference in shape between lower hemisphere 223L of spherical material 223 prior to the forging process, and spherical surface 230S of the final shoe is small, and the spring back effect is reduced or eliminated. Accordingly, spherical surface 230S of shoe 230 may have relatively accurate dimensions. However, a considerable amount of upper hemisphere 223U is deformed into bottom plane surface 230P. Thus, the dimensional accuracy of bottom plane surface 230P of shoe 230 is reduced due to the spring back effect. In addition, the preparation of spherical material 223 is time consuming and expensive.